1. Field of the Invention
The present invention relates to surface acoustic wave devices and methods relating to such devices, and specifically relates to devices and methods for achieving low loss characteristics and for reducing or cancelling undesirable reflections.
2. Description of the Prior Art
Surface acoustic wave (SAW) devices are well known in the prior art. Typically, a surface acoustic wave device is characterized by an input transducer arranged on a piezoelectric surface, with an output transducer spaced from the input transducer for detecting and processing a surface acoustic wave launched by the input transducer along the piezoelectric surface. A wide variety of surface acoustic wave devices have been devised for accomplishing a number of electronic circuit functions.
The typical input transducer for a surface acoustic wave device launches a surface acoustic wave in two directions. Multistrip couplers can be configured which change the track (path) and direction of the surface acoustic wave launched by the input transducer, permitting all of the energy of the wave launched in both directions to be ultimately directed into the output transducer. See, for example, the following literature reference describing the use of multistrip couplers for these purposes: "Reflecting Trackchanger: New Acoustic-Surface-Wave Component for Folding Long Delay Lines onto Small Substrates," F. G. Marshall, Electronic Letters, Vol. 8, pp. 8-9, 1972; "Therory and Design of the Surface Acoustic Wave Multistrip Coupler," F. G. Marshall et al., IEEE Transactions on Sonics and Ultrasonsics, Vol. SU-20, No. 2, p.24, April 1973; "Surface Acoustic Wave Multistrip Components and Their Applications," F. G. Marshall et al., IEEE Transactions on Sonics and Ultrasonics, Vol SU-20, No. 2, p.134, April 1973; "A New Multistrip Acoustic Surface Wave Filter," M. Feldmann et al., 1974 Ultrasonics Symposium Proceedings, IEEE Cat. #74 CHO 896-ISU," p.157; "Surface Acoustic Wave Ring Filter," F. Sandy et al., 1976 Ultrasonics Symposium Proceedings, IEEE Cat. No. 76 CH1120-5SU, p.391; and "Design of Multistrip Arrays," M. Feldmann et al., 1977 IEEE Ultrasonics Symposium Proceedings IEEE Cat. #77CH1264-ISU, p.686.
As is discussed by M. F. Lewis, et al. in an article entitled "Recent Developments in SAW Devices," IEE Proceedings, Vol. 131 Part A, June 1984, a serious problem encountered in SAW devices and particularly in ring loop devices as described above, arises from the triple-transit signals derived from multiple reflections of surface acoustic waves between the input and output transducers. The causes for such undesirable signals are described in that article.